Echinacea and slugs

I am more than usually plagued with slugs so that there are some plants that they just eat the tops off as they come through the ground in spring. Since other people can grow the same plants that I can't grow, I wonder if there is something that my plants are short of that causes them to be so susceptible? My biggest problem is Echinacea but that's not the only one. Thank you, Angela.

Thank you. I do work pretty hard to keep on top of the slugs. I've also several books about them. Years ago I used slug pellets but these days that's a 'no no'. I'm out most evenings with a bucket of soapy water and my rubber gloves but other than stand there all night I have to admit I'm losing the battle. I've just now bought a soil testing kit so will see where that gets me. One problem is that we've had hardly any frost this winter and the slugs have carried on breeding throughout.